Thanks to advances in semiconductor technology, efficiency of light emitting diodes (LEDs) has remarkably improved. LEDs are environmentally friendly as well as economical because of longer lifespan and lower energy consumption than existing lighting devices such as incandescent lamps or fluorescent lamps. Due to these advantages, LEDs are attracting attention as a light source to replace traffic lights or backlights of flat panel display devices such as liquid crystal displays (LCDs).
When LEDs are used as lighting devices, the LEDs are connected in series or in parallel and are turned on and off by a light-emitting element control device. As such, the light-emitting element control device for controlling the LEDs generally rectifies an alternating current (AC) voltage and causes the LEDs to be turned on and off by the rectified ripple voltage.